In recent years, the rapid development of internet and the rise of cloud computing lead to the increasing demands of corporations for information services, and therefore the virtual machine (VM) with satisfactory computing capabilities has been extensively applied in various solutions. For instance, a great number of servers with the VMs are combined through internet, so as to create an integrate computer that is characterized by high-speed computing capabilities and large storage capacity and has gained popularity among the corporations.
To prevent massive loss caused by machine halt or data loss resulting from server failure, a virtual fault tolerance (FT) mechanism may be applied to timely switch to another server and provide services without interruption when a server providing the services fails. FIG. 1 is a schematic diagram illustrating a time delay caused by a virtual FT mechanism. With reference to FIG. 1, a backup cycle of a VM with the FT mechanism can be separated into four phases: a running operation, a backup snapshot operation, a backup transmission operation, and an output operation. If a work load request from a user is received in the first three phases and an output for the user's request is generated, the output is temporarily stored in a buffer memory and is sent out in the last phase, i.e., the output operation. That is to say, in the system featuring the virtual FT mechanism, all of the outputs to the user's request are neither released nor transmitted to the user until the first three phases are completed. Thereby, in the system featuring the virtual FT mechanism, an additional delay time is caused. When processing a work load request being sensitive to the time delay, e.g., online games or real-time trading, the response time of the system cannot be guaranteed; what is more, the issue of internet disconnection or transaction failure may arise accordingly. Hence, a method of controlling the delay time in a system featuring the virtual FT mechanism is required for satisfying such work load requests.